Turbofans are a type of gas turbine engine commonly used in aircraft, such as jets. The turbofan generally includes high and low pressure compressors, high and low pressure turbines, high and low spool shafts, a fan, and a combustor. The high-pressure compressor (HPC) is connected to the high-pressure turbine (HPT) by the high spool rotatable shaft, and together act as a high-pressure system. Likewise, the low-pressure compressor (LPC) is connected to the low-pressure turbine (LPT) by the low spool rotatable shaft, and together act as a low-pressure system. The low spool shaft is housed within the high spool shaft and is connected to the fan such that the HPC, HPT, LPC, LPT, and high and low spool shafts are coaxially aligned.
Air is drawn into the jet turbine engine by the fan and the HPC. The HPC increases the pressure of the air drawn into the system. The high-pressure air then enters the combustor, which burns fuel and emits exhaust gas. The exhaust gas flows from the combustor into the HPT where it rotates the high spool shaft to drive the HPC. After the HPT, the exhaust gas is exhausted to the LPT. The LPT uses the exhaust gas to turn the low spool shaft, which powers the LPC and the fan to continually bring air into the system. Air brought in by the fan bypasses the HPT and LPT and acts to increase the engine's thrust, driving the jet forward.
In order to support the high and low pressure systems, bearings are located within the jet turbine engine to help distribute the load created by the high and low pressure systems. The bearings are connected to an engine casing that houses a mid-turbine frame located between the HPT and the LPT by bearing support structures. The bearing support structures can be, for example, bearing cones. The load from the bearing support structures are transferred to the engine casing through the mid-turbine frame. Decreasing the weight of the engine casing can significantly increase the efficiency of the jet turbine engine and the jet itself. Additionally, maintaining the sealing continuality between the HPT and the mid-turbine frame, and between the LPT and the mid-turbine frame, reduces leakage and also improves the efficiency of the jet turbine engine.